KR20100014557A - Method for forming silicon nitride film, method for manufacturing nonvolatile semiconductor memory device, nonvolatile semiconductor memory device and plasma processing apparatus - Google Patents

Abstract

A plasma processing apparatus (100) introduces microwaves into a chamber (1) by a flat antenna (31) which has a plurality of holes. A material gas, which contains a nitrogen-containing compound and a silicon-containing compound, is introduced into the chamber (1) by using the plasma processing apparatus, and plasma is generated by the microwaves. Then, a silicon nitride film is deposited by the plasma on a surface of a body to be processed. The trap density of the silicon nitride film is controlled by adjusting the conditions of the plasma CVD process.

Description

METHOD FOR FORMING SILICON NITRIDE FILM, METHOD FOR MANUFACTURING NONVOLATILE SEMICONDUCTOR MEMORY DEVICE, NONVOLATILE SEMICONDUCTOR MEMORY DEVICE AND PLASMA PROCESSING

The present invention relates to a method of forming a silicon nitride film which forms a silicon nitride film useful as a charge storage layer of a nonvolatile semiconductor memory device by a plasma CVD (chemical vapor deposition) method, and a nonvolatile semiconductor memory device using the same. A manufacturing method and a nonvolatile semiconductor memory device.

Currently, as a nonvolatile semiconductor memory device represented by EEPROM (Electrically Erasable and Programmable ROM) capable of electrically rewriting operation, there are SONOS (Silicon-Oxide-Nitride-Oxide-Silicon) type and MONOS (Metal-Oxide-Nitride-Oxide-). There is a layered structure called a silicon type. In these types of nonvolatile semiconductor memory devices, information is held by using a silicon nitride film (Nitride) held between silicon dioxide films (Oxide) as a charge storage layer. That is, in the nonvolatile semiconductor memory device, by applying a voltage between the semiconductor substrate (Silicon) and the control gate electrode (Silicon or Metal), electrons are injected into the silicon nitride film of the charge storage layer to store data or silicon nitride The electrons accumulated in the film are removed to save and erase the data.

As a technique for forming a silicon nitride film as a charge storage layer of a nonvolatile semiconductor memory device, Japanese Patent Laid-Open No. 5-145078 (Patent Document 1) discloses dichloromethane when a silicon nitride film is formed between a tunnel oxide film and a top oxide film. A method for forming a silicon nitride film using silane (SiH ₂ C1 ₂ ) and ammonia (NH ₃ ) as a raw material gas, and forming a flow rate ratio SiH ₂ C1 ₂ / NH ₃ by a reduced pressure CVD method under a condition of 1/10 or less It is.

However, with the recent high integration of semiconductor devices, the device structure of nonvolatile semiconductor memory devices has also been rapidly miniaturized. In order to miniaturize a nonvolatile semiconductor memory device, it is necessary to improve the charge accumulation capability of the silicon nitride film which is a charge accumulation layer in each nonvolatile semiconductor memory device, and to improve data retention performance. The charge accumulation capability of this silicon nitride film is related to the density of the trap which is the charge trapping center in the film. Therefore, it is considered to be effective to use a silicon nitride film having a high trap density as a charge storage layer as one means of improving the data retention performance of the nonvolatile semiconductor memory device.

However, in the conventional film forming method by reduced pressure CVD or thermal CVD, it is technically difficult to control the trap density in the film during the formation of the silicon nitride film, and it is not possible to form a silicon nitride film having a desired trap density. For example, in the method of forming the silicon nitride film disclosed in Patent Document 1, since the trap density of the silicon nitride film cannot be directly controlled, an intermediate portion of these films is used for the purpose of increasing the trap density at the interface between the silicon nitride film and the top oxide film. The transition layer containing much Si is provided in this. Furthermore, in Patent Document 1, in order to form this transition layer, a method of controlling the supply timing of the source gas in a complicated order is employed. Specifically, in the technique disclosed in Patent Literature 1, the supply of ammonia is first stopped at the end of film formation of the silicon nitride film, and the supply of dichlorosilane is stopped after the remaining ammonia is consumed. Thereafter, when the top oxide film is formed, first, only nitrous oxide is supplied, and after a predetermined time, silane is supplied to start deposition of the top oxide film.

However, in the method of controlling the supply timing of the source gas as in Patent Document 1, since the film quality is greatly changed due to a slight timing difference, it is considered impossible to form a silicon nitride film having a desired trap density with high reproducibility. .

An object of the present invention is to provide a method for forming a silicon nitride film which can control the trap density of the silicon nitride film to be formed to a desired size.

Another object of the present invention is to provide a non-volatile semiconductor memory device having a silicon nitride film whose charge accumulation performance is controlled and excellent in data retention performance.

According to the first aspect of the present invention, a method of forming a silicon nitride film in which a raw material gas containing a nitrogen-containing compound and a silicon-containing compound is plasma formed by microwaves and a silicon nitride film is deposited on a substrate by plasma CVD using the plasma. The plasma processing such that the substrate is set in the processing chamber of the plasma processing apparatus for introducing microwaves into the processing chamber by a planar antenna having a plurality of holes, and the magnitude of the trap density of the silicon nitride film deposited is controlled to a predetermined value. Provided is a method of forming a silicon nitride film including controlling a condition of plasma CVD in an apparatus to deposit a silicon nitride film on a substrate.

In the first aspect, the plasma is treated at a processing pressure within the range of 1 Pa to 1333 Pa by using ammonia (NH ₃ ) as the nitrogen-containing compound and disilane (Si ₂ H ₆ ) as the silicon-containing compound. The silicon nitride film can be formed by plasma CVD in a condition of generating. In this case, the flow rate ratio (NH ₃ flow rate / Si ₂ H ₆ flow rate) of the ammonia (NH ₃ ) and the disilane (Si ₂ H ₆ ) in the source gas may be in the range of 0.1 to 1000. In addition, the trap density of the silicon nitride film can be distributed within the range of 1 × 10 ¹⁷ to 5 × 10 ¹⁷ cm ⁻³ eV ⁻¹ in the thickness direction thereof. In this case, it is preferable that the film thickness of the said silicon nitride film exists in the range of 1-20 nm.

Further, in the first aspect, at a processing pressure within the range of 0.1 Pa to 500 Pa, using nitrogen (N ₂ ) as the nitrogen-containing compound, and disilane (Si ₂ H ₆ ) as the silicon-containing compound. The silicon nitride film may be formed by plasma CVD in a condition of generating a plasma. In this case, the flow rate ratio (N ₂ flow rate / Si ₂ H ₆ flow rate) of the nitrogen (N ₂ ) and the disilane (Si ₂ H ₆ ) in the source gas may be in the range of 0.1 to 5000.

Moreover, from a said 1st viewpoint, process temperature can be made into the temperature within the range of 300 degreeC-600 degreeC.

According to the second aspect of the present invention, a method of forming a silicon nitride film in which a source gas containing a nitrogen-containing compound and a silicon-containing compound is plasmalized by microwave, and a silicon nitride film is deposited on a substrate by plasma CVD using the plasma. A target object is set in a processing chamber of a plasma processing apparatus that introduces microwaves into the processing chamber by a planar antenna having a plurality of holes, and in the plasma processing apparatus, the substrate surface is formed by plasma CVD under a first condition. Depositing a first silicon nitride film having a first trap density, and in the plasma processing apparatus, different from the first trap density on the first silicon nitride film by plasma CVD under a second condition different from the first condition. Silicon nitride comprising depositing a second silicon nitride film of a second trap density This forming method is provided.

In the second aspect, the first silicon nitride film uses ammonia (NH ₃ ) as the nitrogen-containing compound and disilane (Si ₂ H ₆ ) as the silicon-containing compound, in the range of 1 Pa to 1333 Pa. as contained in a formed by generating a plasma in the processing pressure, the second silicon nitride film, and using a nitrogen (N ₂₎ as the nitrogen-containing compound, the silicon compound used for die-silane (Si ₂ H ₆₎ And generating plasma at a processing pressure within the range of 0.1 Pa to 500 Pa. Further, at least one trap density of the first silicon nitride film and the second silicon nitride film can be distributed within the range of 1 × 10 ¹⁷ to 5 × 10 ¹⁷ cm ^-3 eV ^{-1 in} the thickness direction thereof. have. In this case, it is preferable that at least one film thickness of the said 1st silicon nitride film and said 2nd silicon nitride film is in the range of 1-20 nm. In addition, the deposition of the first silicon nitride film and the deposition of the second silicon nitride film can be performed alternately.

According to a third aspect of the present invention, there is provided a laminate of a plurality of insulating films including a silicon nitride film as a charge storage layer having a charge retention capability on a channel formation region of a semiconductor substrate, and a gate electrode on the laminate. A method of manufacturing a nonvolatile semiconductor memory device including forming the silicon nitride film, wherein the silicon nitride film is formed by plasma-forming a source gas containing a nitrogen-containing compound and a silicon-containing compound by microwaves, and the semiconductor substrate by plasma CVD using the plasma. And a method of depositing a semiconductor substrate in a processing chamber of a plasma processing apparatus which introduces microwaves into the processing chamber by a planar antenna having a plurality of holes, and the silicon nitride film to be deposited. The magnitude of the trap density is controlled to a predetermined value. The lock, the manufacturing method of the nonvolatile semiconductor memory device including the control of the plasma CVD conditions of the above plasma treatment apparatus to depositing the silicon nitride film on a semiconductor substrate.

According to a fourth aspect of the present invention, there is provided a laminate of a plurality of insulating films including a semiconductor substrate having a channel formation region on its main surface, a silicon nitride film formed as a charge storage layer having charge retention capability formed on the channel formation region, In a nonvolatile semiconductor memory device having a gate electrode formed on the laminate, the silicon nitride film plasmas a source gas containing a nitrogen-containing compound and a silicon-containing compound by microwaves, and applies the plasma CVD using the plasma. Formed by a method of depositing a semiconductor substrate on the semiconductor substrate, and the method of depositing a semiconductor substrate in a processing chamber of a plasma processing apparatus that introduces microwaves into the processing chamber by a planar antenna having a plurality of holes. The trap density of the silicon nitride film has a predetermined value. In order to be controlled, a nonvolatile semiconductor memory device is provided which includes depositing a silicon nitride film on a semiconductor substrate by controlling the conditions of plasma CVD in the plasma processing apparatus.

According to a fifth aspect of the present invention, there is provided a processing chamber for processing a target object using plasma, a planar antenna having a plurality of holes for introducing microwaves into the processing chamber, and a gas supply for supplying a source gas into the processing chamber. A source gas containing a mechanism, an exhaust mechanism for evacuating the inside of the processing chamber under reduced pressure, a temperature regulating mechanism for adjusting the temperature of the target object, and a nitrogen-containing compound and a silicon-containing compound are introduced into the processing chamber by the planar antenna. In the plasma processing apparatus described above, when the silicon nitride film is deposited on the substrate by plasma CVD using the plasma and the silicon nitride film is deposited on the substrate, the trap density of the deposited silicon nitride film is controlled to a predetermined value. A plasma processing apparatus comprising a control unit for controlling conditions of plasma CVD. Is provided.

MEANS TO SOLVE THE PROBLEM This inventor can control the magnitude | size of the trap density of the silicon nitride film formed by changing the conditions of plasma CVD film-forming using the plasma processing apparatus which introduces a microwave into a process chamber by the planar antenna which has a some hole. Found that. In the present invention, the silicon nitride film is deposited on the substrate by controlling the conditions of plasma CVD in the plasma processing apparatus so that the magnitude of the trap density of the silicon nitride film deposited is controlled to a predetermined value. A silicon nitride film having a desired trap density can be formed. In addition, the silicon nitride film having the desired trap density thus formed can be used as an insulating film when fabricating various semiconductor devices, and in particular, as a charge storage layer of a nonvolatile semiconductor memory device, thereby providing a nonvolatile memory having excellent data retention performance. A semiconductor memory device can be realized.

In addition, according to the present invention, by controlling the conditions of plasma CVD and stacking silicon nitride films having different trap densities, various band engineering is possible in the nonvolatile semiconductor memory device, and the nonvolatile semiconductor memory excellent in data retention characteristics. The device can be manufactured. In addition, by stacking silicon nitride films having different trap densities in this manner, two or more silicon nitride films having different trap densities can be formed in the chamber of a single plasma processing apparatus without exposing to an atmospheric state. Design can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows schematic structure of an example of the plasma processing apparatus suitable for implementation of the silicon nitride film formation method of this invention.

FIG. 2 is a plan view illustrating the planar antenna of the plasma processing apparatus of FIG. 1. FIG.

3 is a block diagram illustrating a configuration of a control unit of the plasma processing apparatus of FIG. 1.

4 is a flowchart showing an outline of a procedure of a method of forming a silicon nitride film according to the first embodiment of the present invention.

5 shows PYS measurement results of a silicon nitride film (film thickness of 3 nm).

6 shows PYS measurement results of a silicon nitride film (film thickness of 10 nm).

7 shows PYS measurement results of a silicon nitride film and a hydrogen terminated Si (100) plane;

8 is a diagram showing a depth direction distribution of electron occupancy defect density of a silicon nitride film.

9 shows the chemical composition profile of a silicon nitride film measured by XPS analysis.

Fig. 10 is a diagram showing the depth direction distribution of electron occupancy defects of the silicon nitride film of test section I by LPCVD.

11 is a diagram showing a depth direction distribution of an electron-occupying defect density of a silicon nitride film of test section J. FIG.

Fig. 12 shows the XPS analysis results of the silicon nitride film of test section I by LPCVD.

The figure which shows the XPS analysis result of the silicon nitride film of test division J. FIG.

14 is a cross-sectional view illustrating a schematic configuration of a nonvolatile semiconductor memory device according to one embodiment of the present invention;

15 is a cross-sectional view showing the manufacturing process of the nonvolatile semiconductor memory device using the method for forming the silicon nitride film according to the first embodiment of the present invention.

16 is a cross sectional view showing the manufacturing process of the nonvolatile semiconductor memory device using the method for forming the silicon nitride film according to the first embodiment of the present invention.

17 is a cross sectional view showing the manufacturing process of the nonvolatile semiconductor memory device using the method for forming the silicon nitride film according to the first embodiment of the present invention.

18 is a cross sectional view showing the manufacturing process of the nonvolatile semiconductor memory device using the method for forming the silicon nitride film according to the first embodiment of the present invention.

19 is a cross sectional view showing the manufacturing process of a nonvolatile semiconductor memory device using the silicon nitride film forming method according to the first embodiment of the present invention.

20 is a cross-sectional view showing the manufacturing process of the nonvolatile semiconductor memory device using the method for forming the silicon nitride film according to the first embodiment of the present invention.

21 is a flowchart showing an outline of a procedure of a method of forming a silicon nitride film according to the second embodiment of the present invention.

Fig. 22 is an explanatory diagram showing a schematic configuration of a nonvolatile semiconductor memory device according to another embodiment of the present invention.

23 shows XPS analysis results of a silicon nitride film.

EMBODIMENT OF THE INVENTION Hereinafter, the preferred embodiment of this invention is described, referring drawings.

<First Embodiment>

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows schematic structure of an example of the plasma processing apparatus suitable for implementation of the silicon nitride film formation method of this invention, FIG. 2 is a top view which shows the planar antenna of the plasma processing apparatus of FIG. It is a block diagram which shows the structure of the control part of 1 plasma processing apparatus.

The plasma processing apparatus 100 generates a plasma by introducing microwaves into the processing chamber with a radial line slot antenna (RLSA), which is a planar antenna having a plurality of slot-shaped holes, to generate plasma. It is comprised as an RLSA microwave plasma processing apparatus which can generate the microwave excited plasma of an electron temperature. In the plasma processing apparatus 100, it is possible to treat with a plasma having a plasma density of 1 × 10 ¹⁰ m to 5 × 10 ¹² / cm ³ , and having a low electron temperature of 0.7 to 2 eV. For this reason, the plasma processing apparatus 100 can be used suitably for the film-forming process of the silicon nitride film by plasma CVD in the manufacturing process of various semiconductor devices.

The plasma processing apparatus 100 includes a chamber (process chamber) 1 that is hermetically sealed, a gas supply mechanism 18 for supplying gas into the chamber 1, and an exhaust device for evacuating the inside of the chamber 1 under reduced pressure ( 24, the microwave introduction mechanism 27 which is provided in the upper part of the chamber 1, and introduces a microwave into the chamber 1, and the control part 50 which controls each structure part of these plasma processing apparatus 100 is main. It is equipped as a structure.

The chamber 1 is a grounded substantially cylindrical container, and has the bottom wall 1a and the side wall 1b which consist of aluminum, for example. In addition, the chamber 1 may be a container of a square cylinder shape.

Inside the chamber 1, a mounting table 2 for horizontally supporting a silicon wafer (hereinafter referred to simply as a “wafer”) W as an object to be processed is provided. The mounting table 2 is made of a ceramic having high thermal conductivity, such as AlN. This mounting table 2 is supported by a cylindrical support member 3 extending upward from the bottom center of the exhaust chamber 11. The support member 3 is also made of a ceramic having high thermal conductivity, such as AlN.

In addition, the mounting table 2 is provided with a covering 4 for covering the outer edge portion and guiding the wafer W. As shown in FIG. This covering 4 is an annular member composed of any one material of, for example, quartz, AlN, Al ₂ O ₃ , or SiN.

In the mounting table 2, a heater 5 of resistance heating type as a temperature control mechanism is embedded. The heater 5 heats the mounting table 2 by being fed from the heater power supply 5a, and uniformly heats the wafer W which is the substrate to be processed by the heat.

In addition, the mounting table 2 is provided with a thermocouple (TC) 6. Based on the temperature detected by this thermocouple 6, the wafer W can be controlled in the range from room temperature to 900 degreeC, for example.

The mounting table 2 also has a wafer support pin (not shown) for supporting and lifting the wafer W. As shown in FIG. Each wafer support pin is provided in such a manner that it can be driven against the surface of the mounting table 2.

The circular opening part 10 is formed in the substantially center part of the bottom wall 1a of the chamber 1. The bottom wall 1a is provided with the exhaust chamber 11 which communicates with this opening part 10 and protrudes downward. An exhaust pipe 12 is connected to the exhaust chamber 11, and is connected to the exhaust device 24 through the exhaust pipe 12.

At the upper end of the side wall 1b which forms the chamber 1, the annular plate 13 which has a function as a lid which opens and closes the chamber 1 is arrange | positioned. The lower part of the inner periphery of the plate 13 protrudes toward the inner side (in-chamber space) to form an annular support 13a.

The plate 13 is provided with the gas introduction part 14 which annularly forms as a 1st gas introduction part. In addition, the side wall 1b of the chamber 1 is provided with the gas introduction part 15 cyclic | annular as a 2nd gas introduction part. That is, these gas introduction parts 14 and 15 are provided in two stages up and down. Predetermined gas is supplied to the gas introduction parts 14 and 15 from the gas supply mechanism 18. In addition, the gas introduction parts 14 and 15 may be a nozzle shape or a shower head shape. In addition, the gas introduction part 14 and the gas introduction part 15 may be used as a single shower head.

In addition, the sidewall 1b of the chamber 1 has a carrying in / out port for carrying in and out of the wafer W between a transfer chamber (not shown) adjacent to the plasma processing apparatus 100 ( 16 and the gate valve 17 which opens and closes this carry-in / out port 16 are provided.

The gas supply mechanism 18 includes, for example, a nitrogen-containing gas (N-containing gas) source 19a, a silicon-containing gas (Si-containing gas) source 19b, an inert gas supply source 19c, and a cleaning gas source 19d. Have The nitrogen-containing gas supply source 19a is connected to the gas introduction part 14 of the upper end. In addition, the silicon-containing gas supply source 19b, the inert gas supply source 19c, and the cleaning gas source 19d are connected to the lower gas introduction part 15. On the other hand, the gas supply mechanism 18 may have a purge gas supply source etc. which are used when replacing the atmosphere in a chamber, for example as a gas supply source not shown in the figure other than the above.

Examples of the nitrogen-containing gas film forming raw material gas, for example, may be used a nitrogen gas (N _2), such as ammonia (NH _3), MMH (monomethyl hydrazine), such as a hydrazine derivative. Further, as the other film-forming raw material gas of a silicon-containing gas, may for example take advantage of a silane (SiH _4), dimethyl silane _{(Si 2 H 6), TSA} ( trimethyl silyl amine) and the like. Among these, silane (Si ₂ H ₆ ) is particularly preferable. Examples of the inert gas can be used, and for example, N ₂ gas or a rare gas. The rare gas is a gas for plasma excitation, and for example, Ar gas, Kr gas, Xe gas, He gas and the like can be used.

Further, as the cleaning gas, ClF ₃ gas may be used, NF ₃ gas, HC1 gas, Cl ₂ gas and the like. Among them, NF ₃ gas is used in a plasma form.

The nitrogen-containing gas reaches the gas introduction portion 14 through the gas line 20 from the nitrogen-containing gas supply source 19a of the gas supply mechanism 18 and is introduced into the chamber 1 from the gas introduction portion 14. . On the other hand, the silicon-containing gas and the inert gas reach the gas inlet 15 from the silicon-containing gas source 19b and the inert gas source 19c via the gas line 20, respectively, and the chamber from the gas inlet 15. It is introduced in (1). In each gas line 20 connected to each gas supply source, the mass flow controller 21 and the opening / closing valve 22 before and behind it are provided. Such a configuration of the gas supply mechanism 18 enables control of replacement of the gas to be supplied, flow rate, and the like. On the other hand, the rare gas for plasma excitation, such as Ar, is arbitrary gas, It is not necessary to supply simultaneously with film-forming raw material gas, but it is preferable to supply, considering the stable generation of plasma.

The exhaust device 24 includes a high speed vacuum pump such as a turbo molecular pump. The exhaust device 24 is connected to the exhaust chamber 11 of the chamber 1 via the exhaust pipe 12. By operating this exhaust device 24, the gas in the chamber 1 flows uniformly in the space 11a of the exhaust chamber 11 and is exhausted from the space 11a to the outside through the exhaust pipe 12. . As a result, the inside of the chamber 1 can be decompressed at high speed, for example, to 0.133 Pa.

Next, the structure of the microwave introduction mechanism 27 is demonstrated. The microwave introduction mechanism 27 includes a transmission plate 28, a planar antenna 31, a slow wave material 33, a cover 34, a waveguide 37, and a microwave generator 39 as main components.

The transmission plate 28 which transmits microwaves is supported by the support surface 13a provided annularly inside the plate 13. The transparent plate 28 and the support surface 13a are hermetically sealed through the sealing member 29, whereby the inside of the chamber 1 is hermetically maintained. The transmission plate 28 is made of a dielectric such as quartz, ceramics such as Al ₂ O ₃ and AlN.

The planar antenna 31 has a disk shape, and is provided to face the mounting table 2 above the transmission plate 28. In addition, the shape of the planar antenna 31 is not limited to a disk shape, For example, it may be a square plate shape. This planar antenna 31 is hung on the upper end of the plate 13.

The planar antenna 31 is composed of, for example, a copper plate, a nickel plate, a stainless steel plate, or an aluminum plate whose surface is gold or silver plated. The planar antenna 31 has a plurality of slot-like microwave radiation holes 32 for emitting microwaves. The microwave radiation hole 32 is formed through the planar antenna 31 in a predetermined pattern.

The individual microwave radiation holes 32 form an elongated hole as shown in FIG. 2, for example, and two adjacent microwave radiation holes are paired. And the adjacent microwave radiation hole 32 is arrange | positioned in "T" shape, for example. In addition, the microwave radiation hole 32 arrange | positioned in combination with a predetermined shape (for example, T-shape) in this way is further arrange | positioned in concentric circular shape as a whole.

The length and arrangement interval of the microwave radiation holes 32 are determined depending on the wavelength λg of the microwaves. For example, the space | interval of the microwave radiation hole 32 is arrange | positioned so that it may become (lambda) g / 4 from (lambda) g. In FIG. 2, the space | interval of the adjacent microwave radiation hole 32 formed concentrically is shown by (triangle | delta) r. In addition, the shape of the microwave radiation hole 32 may be another shape, such as circular shape and circular arc shape. In addition, the arrangement | positioning form of the microwave radiation hole 32 is not specifically limited, It can also arrange | position in spiral shape, radial shape, etc. besides concentric circles.

On the upper surface of the planar antenna 31, a slow wave material 33 having a dielectric constant larger than that of vacuum is provided. The slow wave material 33 has a function of adjusting the plasma by shortening the wavelength of the microwave because the wavelength of the microwave becomes long in vacuum.

The planar antenna 31 and the transmission plate 28 and the slow wave material 33 and the planar antenna 31 may be in contact or separated from each other, but are preferably in contact with each other.

In the upper part of the chamber 1, the cover 34 which has a waveguide function which consists of metal materials, such as aluminum, stainless steel, and copper, is provided so that these planar antennas 31 and the slow wave material 33 may be covered. The upper end of the plate 13 and the cover 34 are sealed by the sealing member 35. The cooling water flow path 34a is formed inside the cover 34. By cooling the cooling water in the cooling water flow path 34a, the cover 34, the slow wave material 33, the planar antenna 31, and the transmission plate 28 can be cooled. On the other hand, the cover 34 is grounded.

An opening 36 is formed in the center of the upper wall (ceiling portion) of the cover 34, and a waveguide 37 is connected to the opening 36. The other end side of the waveguide 37 is connected to a microwave generator 39 that generates microwaves through the matching circuit 38.

The waveguide 37 extends in a horizontal direction connected to the coaxial waveguide 37a having a circular cross section extending upward from the opening 36 of the cover 34, and connected to the upper end of the coaxial waveguide 37a via a mode converter. It has a rectangular waveguide 37b.

The inner conductor 41 extends at the center of the coaxial waveguide 37a. The inner conductor 41 is connected and fixed to the center of the planar antenna 31 at the lower end thereof. By this structure, the microwaves propagate radially efficiently and uniformly through the inner conductor 41 of the coaxial waveguide 37a to the flat waveguide formed by the conductive cover 34 and the planar antenna 31.

By the microwave introduction mechanism 27 of the above-mentioned structure, the microwave which generate | occur | produced in the microwave generator 39 propagates to the flat antenna 31 through the waveguide 37, and also the chamber 1 through the permeable plate 28. Is introduced in the On the other hand, as the frequency of the microwave, for example, 2.45 GHz is preferably used, and in addition, 8.35 GHz, 1.98 GHz and the like can be used.

Each component of the plasma processing apparatus 100 is connected to the control part 50, and is controlled. The control part 50 is equipped with the process controller 51 provided with CPU, the user interface 52 connected to this process controller 51, and the memory | storage part 53 as shown in FIG. In the plasma processing apparatus 100, the process controller 51 includes components (eg, the heater power supply 5a, the gas supply mechanism 18, and the exhaust apparatus) that are related to process conditions such as pressure, temperature, and gas flow rate. (24), the microwave generator 39 and the like).

The user interface 52 has a keyboard for the process manager to perform command input operations and the like for managing the plasma processing apparatus 100, a display for visualizing and displaying the operation status of the plasma processing apparatus 100, and the like. The storage unit 53 stores recipes in which control programs (software), processing condition data, and the like are recorded for realizing various processes executed in the plasma processing apparatus 100 under the control of the process controller 51.

Then, if necessary, an arbitrary recipe is called from the storage unit 53 by an instruction from the user interface 52 and executed by the process controller 51, so that the plasma processing apparatus is controlled under the control of the process controller 51. The desired process at 100 is performed. The recipe such as the control program and the processing condition data may be a computer readable storage medium such as a CD-ROM, a hard disk, a flexible disk, a flash memory, or the like stored in a state, or from another device, for example, on a dedicated line. It is also possible to use the online transmission by sending through the occasional.

In the plasma processing apparatus 100 configured as described above, intact plasma CVD processing to the base film or the like can be performed at a low temperature of 800 ° C or lower. In addition, since the plasma processing apparatus 100 is excellent in the uniformity of plasma, the uniformity of the process can be realized.

In the RLSA type plasma processing apparatus 100 configured as described above, a process of depositing a silicon nitride film on the surface of the wafer W by, for example, the plasma CVD method is performed in the order shown in the flowchart of FIG. 4.

First, the gate valve 17 is opened, the wafer W is loaded into the chamber 1 from the carry-in / out port 16, and it mounts on the mounting table 2 (step S1). Next, the inside of the chamber 1 is evacuated under reduced pressure (step S2). Then, the gas inlet portions 14 and 15 are respectively discharged from the nitrogen-containing gas supply source 19a and the silicon-containing gas supply source 19b of the gas supply mechanism 18 at a predetermined flow rate while evacuating under reduced pressure. It introduces into the chamber 1 through (step S3). In this way, the inside of the chamber 1 is adjusted to predetermined pressure.

Next, a microwave of a predetermined frequency generated at the microwave generator 39, for example, 2.45 GHz, is guided to the waveguide 37 through the matching circuit 38 (step S4). Microwaves guided to the waveguide 37 pass sequentially through the rectangular waveguide 37b and the coaxial waveguide 37a and are supplied to the planar antenna 31 via the inner conductor 41. That is, microwaves propagate in the coaxial waveguide 37a toward the planar antenna 31. Then, the microwaves are radiated from the slot-shaped microwave radiation holes 32 of the planar antenna 31 to the space above the wafer W in the chamber 1 via the transmission plate 28. The microwave output at this time is preferably within the range of 0.14 to 4.19 W / cm 2 as the power density per 1 cm 2 of the planar antenna 31. The microwave output can be selected to be a power density within the above range according to the purpose, for example, in the range of 500 to 5000 W.

Electromagnetics are formed in the chamber 1 by the microwaves radiated from the planar antenna 31 through the transmission plate 28 to the chamber 1, and the nitrogen-containing gas and the silicon-containing gas are respectively converted into plasma. This microwave-excited plasma has a high density of approximately 1 × 10 ¹⁰ to 5 × 10 ¹² / cm ³ and the wafer W by microwaves being emitted from the plurality of microwave radiation holes 32 of the planar antenna 31. In the vicinity, a low electron temperature plasma of about 1.5 eV or less is obtained. The microwave excited high density plasma formed in this way has little plasma damage to a base film. Then, dissociation of the source gas in the plasma proceeds, and reaction of active species such as Si _p H _q , SiH _q , NH _q , and N (where p and q mean an arbitrary number is equal to or below). , Silicon nitride SixN or silicon nitride oxide Si _x O _z N _y having a trap density of a predetermined size, where x, y, z are not necessarily stoichiometrically, and any number that takes different values depending on conditions Thin film) is deposited.

In the present invention, by selecting conditions for plasma CVD film formation using the plasma processing apparatus 100, the trap density of the silicon nitride film to be formed can be controlled to a desired size.

For example, when the trap density in the silicon nitride film formed into a film is made small (for example, trap density is 5 * 10 <^10> ~ 5 * 10 <^12> cm <^2> eV <^-1> by surface density, a 1st condition is selected. Under this first condition, it is preferable to use N ₂ gas as the nitrogen-containing gas and Si ₂ H ₆ gas as the silicon-containing gas. At this time, the flow rate ratio (N ₂ gas flow rate / Si ₂ H ₆ gas flow rate) of the N ₂ gas and the Si ₂ H ₆ gas ranges from 0.1 to 5000 in view of forming a silicon nitride film having a low Si density with a uniform film thickness. It is preferable to set it as inside, and the range of 100-2000 is more preferable. Specifically, the N ₂ gas flow rate is in the range of 10 to 5000 mL / min (sccm), preferably in the range of 100 to 2000 mL / min (sccm), and the Si ₂ H ₆ gas flow rate is 0.5 to 100 mL / The flow rate ratio is set within a range of min (sccm), preferably within a range of 0.5 to 10 mL / min (sccm). Further, in the first condition using the N ₂ gas and Si ₂ H ₆ gas, in order to form a silicon nitride film having a small trap density, it is preferable to set the processing pressure to 0.1 to 500 Pa, and to set it to 1 to 100 Pa. More preferred. Moreover, it is preferable to make the power density of a microwave into 0.41-4.19 W / cm <2> (per 1 cm <2> of areas of the planar antenna 31).

For example, when enlarging the trap density in the silicon nitride film formed into a film (for example, a trap density is in the range of 1 * 10 <^{11> -1} * 10 <^13> cm <^-2> eV <^-1> by surface density, a 2nd condition is selected. Under this second condition, it is preferable to use NH ₃ gas as the nitrogen-containing gas and Si ₂ H ₆ gas as the silicon-containing gas. At this time, the flow rate ratio (NH ₃ gas flow rate / Si ₂ H ₆ gas flow rate) of NH ₃ gas and Si ₂ H ₆ gas is in the range of 0.1 to 1000 from the viewpoint of forming a silicon nitride film having a high Si density with a uniform film thickness. It is preferable to carry out, and the inside of the range of 10-300 is more preferable. Specifically, the flow rate of the NH ₃ gas range of 10 ~ 5000 mL / min (sccm ) in, preferably 100 to a range of 2000 mL / min (sccm) within 0.5 to 100 the flow rate of Si ₂ H ₆ gas The flow rate ratio is set within a range of mL / min (sccm), preferably within a range of 1 to 50 mL / min (sccm). In the second condition using the NH ₃ gas and Si ₂ H ₆ gas, in order to form a silicon nitride film having a large trap density, it is preferable to set the processing pressure to 1 to 1333 Pa, and to set it to 50 to 650 Pa. More preferred. Moreover, it is preferable to make the power density of a microwave into 0.41-4.19 W / cm <2> (per 1 cm <2> of areas of the planar antenna 31).

In addition, by performing plasma CVD on the second condition using the plasma processing apparatus 100, a silicon nitride film having a distribution of trap densities substantially uniform in the thickness direction of the film can be formed. That is, for example, the volume density of the trap at the energy position corresponding to the mid-gap of silicon is distributed in the range of 1 × 10 ¹⁷ to 5 × 10 ¹⁷ cm ⁻³ eV ^{−1 in} the thickness direction of the film. From the interface with the base silicon layer to the surface side, the silicon nitride film in which the volume density of the trap is distributed within the range of 1 × 10 ¹⁷ to 2 × 10 ¹⁷ cm ^-3 eV ^-1 can be formed. In this case, the film thickness of the silicon nitride film formed is preferably in the range of 1 to 20 nm, more preferably in the range of 3 to 15 nm. On the other hand, it can be converted into surface density by multiplying the volume density of the trap by 2/3.

In any of the above first and second conditions, the plasma CVD process temperature is preferably 300 ° C. to 800 ° C., preferably 400 ° C. to 600 ° C., for the temperature of the mounting table 2. It is more preferable to heat. In addition, the gap (interval from the lower surface of the transparent plate 28 to the upper surface of the mounting table 2) G in the plasma processing apparatus 100 is a viewpoint of forming a silicon nitride film with a uniform film thickness and film quality. For example, it is preferable to set about 50-500 mm.

Next, the supply of microwaves is stopped and the formation of the silicon nitride film is finished (step S5). Next, supply of the gas from the gas supply mechanism 18 is stopped (step S6). Then, after the deposition of the silicon nitride film is completed, the wafer W on which the silicon nitride film is formed is taken out from the chamber 1 to finish the processing for one wafer W (step S7).

When the silicon nitride film is formed by plasma CVD using the plasma processing apparatus 100, by depositing the silicon nitride film on the silicon dioxide film (SiO ₂ film), the trap density of the silicon nitride film can be made larger. For this reason, in this embodiment, when the base layer is, for example, a silicon substrate made of single crystal silicon or a polycrystalline silicon layer, it is preferable to form a thin film of SiO ₂ on the surface of the base layer in advance. In this case, the thin film of SiO ₂ may be a natural oxide film, a thermal oxide film, or a plasma oxide film. Further, for example, a chemical oxide may be formed by chemically treating the Si surface with a chemical agent having an oxidation action such as HPM (hydrogen peroxide) or SPM (hydrogen peroxide). As the film thickness of the SiO ₂ thin film placed in advance formed on a surface of the base layer, for example to 0.1 ~ 10㎚ it is preferred, more preferably 0.1 ~ 3㎚.

The trap density of the silicon nitride film formed by the method of forming the silicon nitride film of the present embodiment can be measured using, for example, photoelectric yield spectroscopy (PYS). PYS is a method of irradiating a sample (silicon nitride film) with light of constant energy, and measuring the forward photoelectron amount of photoelectrons emitted by the photoelectric effect as a function of energy of incident light. By this PYS measurement, the defect level density distribution at the interface between the silicon nitride film and the silicon nitride film and the silicon layer can be measured non-destructively and with high sensitivity. Since the photoelectron yield measured in PYS corresponds to the energy integration of the electron occupied state density distribution, the defect level density distribution is derived from the differential PYS spectrum by the method of S. Miyazaki et al. (Microelectron.Eng.48 (1999) 63.). You can ask.

Next, the test result which confirmed the effect of this invention is demonstrated. Using the plasma processing apparatus 100, the silicon nitride film was formed into a film on the p-type silicon substrate (10 ohm * cm) by changing conditions. The silicon nitride film obtained was measured in PYS. PYS measurement was performed by irradiating each silicon nitride film with an ultraviolet-ray using an ultraviolet lamp, and measuring the emitted electron with the photoelectron increase piping. In this test, experiment was carried out about test divisions A to H shown in Table 1 below.

The contents of the plasma CVD conditions shown in Table 1 are as follows.

<Plasma CVD condition 1; N ₂ / Si ₂ H ₆ Gas Meters>

N ₂ gas flow rate; 1200 mL / min (sccm)

Si ₂ H ₆ gas flow rate; 3 mL / min (sccm)

Flow rate ratio (N ₂ / Si ₂ H ₆ ); 400

Processing pressure; 7.6 Pa

Temperature of the mounting table 2; 500 ℃

Microwave power; 2000 W

Microwave power density; 1.67 W / cm 2 (per area 1 cm 2 of planar antenna 31)

<Plasma CVD condition 2; NH ₃ / Si ₂ H ₆ Gas System>

NH ₃ gas flow rate; 800 mL / min (sccm)

Si ₂ H ₆ gas flow rate; 10 mL / min (sccm)

Flow rate ratio (NH ₃ / Si ₂ H ₆ ); 80

Processing pressure; 126 Pa

Temperature of the mounting table 2; 500 ℃

Microwave power; 2000 W

Microwave power density; 1.67 W / cm 2 (per area 1 cm 2 of planar antenna 31)

The content of the pretreatment shown in Table 1 is as follows.

<DHF Processing>

Before plasma CVD, the surface of the silicon substrate was treated with a 1% dilute fluoric acid solution to remove the native oxide film.

<HPM Processing>

Before plasma CVD, the surface of the silicon substrate was treated with a 1% dilute hydrofluoric acid solution to remove the native oxide film, and then treated with 10% HPM (hydrogen peroxide) to form a SiO ₂ film as a chemical oxide film. .

The results of the PYS measurement are shown in FIGS. 5 and 6. FIG. 5 shows the result that the film thickness of the silicon nitride film is 3 nm, and FIG. 6 shows the result that the film thickness of the silicon nitride film is 10 nm. The silicon nitride film formed under plasma CVD condition 2 using ammonia as the source gas (test sections E, F, G, and H) is a silicon nitride film formed under plasma CVD condition 1 using nitrogen as the source gas (test sections A, B, Compared with C and D), the photoelectron yield was high and the trap density was suggested.

In addition, the difference in the density of defect levels due to the difference in plasma CVD conditions is 3 nm (test division A, B, E, F) was remarkable. In addition, as shown in FIG. 5, when the test sections E and F in which the silicon nitride film has a thickness of 3 nm are compared, HPM treatment is performed as a pretreatment even if the plasma CVD conditions are the same, and chemical oxide SiO ₂ is applied to the surface of the silicon substrate. By forming the layer, it has been suggested that a silicon nitride film having a large defect level density can be obtained.

Next, the chemical composition distribution and the defect state density distribution were quantified with respect to the silicon nitride film formed by plasma CVD using the plasma processing apparatus 100, and the correlation between them was investigated. After HPM treatment was performed on the Si (100) surface of the p-type silicon substrate (10? cm) to form a chemical oxide SiO ₂ layer, a silicon nitride film having a thickness of 11.4 nm was formed at a temperature of 400 ° C. The plasma CVD conditions are as follows.

<Plasma CVD condition 3; NH ₃ / Si ₂ H ₆ Gas System>

NH ₃ gas flow rate; 800 mL / min (sccm)

Si ₂ H ₆ gas flow rate; 16 mL / min (sccm)

Flow rate ratio (NH ₃ / Si ₂ H ₆ ); 50

Processing pressure; 126 Pa

Temperature of the mounting table 2; 400 ℃

Microwave power; 2000 W

Microwave power density: 1.67 W / cm 2 (per area 1 cm 2 of planar antenna 31)

The formed silicon nitride film was etched with dilute fluoric acid to form a thin film, and PYS measurement and X-ray electron spectroscopy (XPS) measurement were performed in each etching process. The result of PYS measurement of the produced silicon nitride film [SiNx / Si (100)] and the hydrogen termination Si (100) [H-p + Si (100)] after etching for 60 second is shown in FIG. As shown in FIG. 7, in the silicon nitride film [SiNx / Si (100)], electron occupancy defects (traps) exist in an energy region corresponding to the Si band gap, and therefore, an energy region (<5.15) lower than that of the Si valence band top (Ev). eV), the photoelectron yield from the silicon nitride film was found to be remarkable and large compared to the hydrogen terminated Si (100).

Moreover, the result of having estimated the depth direction distribution of the electron occupancy defect from the amount of change of the optoelectronic yield in each etching process is shown in FIG. As shown in Fig. 8, the electron occupancy defect density at the shallow energy position (E-Ev = 0.28 eV) of 0.28 eV from the Si valence band upper end (Ev) is the maximum (~ 6.O x 10 O near the Si substrate interface. ¹⁸ cm ^-3 eV ^-1 , and it was confirmed to be the minimum (~ 3.2 x 10 ¹⁷ cm ^-3 eV ^-1 ) in the region of about 4 nm from the Si substrate interface. In addition, at the energy position (E-Ev = 0.56 eV) corresponding to the mid gap of silicon, the electron occupancy defect density near the Si interface is remarkably decreased, while in the silicon nitride film, the electron occupancy defect similar to that of the valence band side. Density distribution was obtained.

9 shows the chemical composition profile of the silicon nitride film measured by XPS analysis. In FIG. 9, it turns out that oxygen atom is remarkably diffused and mixed in the silicon nitride film in the area | region near the surface of a silicon nitride film, and the area | region within about 3 nm of thickness from an Si substrate interface. The oxidation on the surface side is due to natural oxidation, and the Si substrate interface side is considered to be due to the interfacial reaction between the chemical oxide SiO ₂ layer and the silicon nitride film.

When the result of the energy position (E-Ev = 0.56 eV) corresponding to the midgap of silicon in FIG. 8 is compared with the chemical composition profile of the silicon nitride film by XPS measurement shown in FIG. 9, it is about 2 from the Si substrate interface. It can be seen that the region where the electron occupancy defects are increasing locally in the vicinity of nm corresponds to the vicinity of the interface between the chemical oxide SiO ₂ layer and the silicon nitride film. As described above, in the silicon nitride film formed by the plasma CVD condition 3 using the plasma processing apparatus 100, the electron occupancy in the film near the interface between the chemical oxide SiO ₂ layer and the silicon nitride film in which oxygen atoms are diffused and mixed. It was found that the defect density significantly increased.

Next, the depth direction distribution of the electron occupancy defect density at the energy position corresponding to the midgap of silicon was measured with respect to the two silicon nitride films (test divisions I and J) formed under different conditions. 11 is shown. In addition, the result of having measured the chemical composition profile of the silicon nitride film of test division I and J by XPS analysis to FIG. 12 and 13 is shown. A test section I (comparative example) is a 13 nm thick silicon nitride film formed by LPCVD (Low Pressure Chemical Vapor Deposition) under the following conditions, and a section J is the plasma treatment apparatus 100 using the plasma processing apparatus 100. A silicon nitride film having a thickness of 4.1 nm formed under CVD condition 2. In both test divisions I and J, a 3 nm-thick chemical oxide SiO ₂ layer was formed on the Si (100) plane by HPM treatment under the above conditions, and CVD was performed thereon.

<LPCVD condition>

SiH ₂ Cl ₂ gas flow rate; 10 mL / min (sccm)

NH ₃ gas flow rate; 1000 mL / min (sccm)

Flow rate ratio (NH ₃ / SiH ₂ Cl ₂ ); 100

Processing pressure; 133 Pa

Temperature of the mounting table 2; 800 ℃

In Fig. 10, for the silicon nitride film of the test section I (comparative example) formed by LPCVD, the energy position (E-Ev = 0.56 eV) corresponding to the mid gap of silicon and 0.84 from the upper end of the Si valence band (Ev) The volume density of the electron occupancy defects at the shallow energy position of the eV (E-Ev = 0.84 eV) is shown. From this FIG. 10, the silicon nitride film of test section I formed by LPCVD has an energy position (E-Ev = 0.56 eV) corresponding to the midgap of silicon in a range of about 10 nm from the Si (100) interface. Can be read as having an electron occupancy defect density of 1 m) of approximately 1 × 10 ¹⁷ cm ³ eV ⁻¹ or less. That is, the silicon nitride film of the test division I is concerned that the electron occupancy defect density is low overall, and that charge dropping is likely to occur.

On the other hand, in test section J which is a condition of the present invention formed under plasma CVD condition 2 using ammonia and disilane as source gas, as shown in FIG. 11, electron occupancy defects are distributed substantially uniformly in the film thickness direction. It was confirmed that the absolute value was also large compared to the test section I. That is, the silicon nitride film of the test section J has an electron occupancy defect density at an energy position corresponding to the midgap of silicon within the range of 1 × 10 ¹⁷ to 5 × 10 ¹⁷ cm ^-3 eV ^{-1 in} the thickness direction of the film. It is evenly distributed. In this way, in the silicon nitride film of the test section J having an even and large absolute trap density in the thickness direction of the film, the injected charge is retained even in the center portion of the film, so that a drop in charge is less likely to occur and the charge accumulation capacity I think this is high. Therefore, the silicon nitride film controlled so that such electron-occupancy defects become uniform in the film thickness direction can be expected as an excellent charge accumulation capability by using it as a charge accumulation layer of a semiconductor memory device having a SONOS (MONOS) structure.

In addition, the silicon nitride film of the test division J has a thickness of 4 nm, as shown in FIG. In the range, the electron occupancy defect density at an energy position corresponding to the midgap of silicon is distributed in a narrow range of 1 × 10 ¹⁷ to 2 × 10 ¹⁷ cm ^-3 eV ^-1 . In other words, a portion having a very uniform trap density distribution can be formed in the silicon nitride film, and even if the film thickness is thin in this manner, a sufficiently high charge accumulation capacity can be exhibited. Accordingly, by using the silicon nitride film in which the electron occupancy defects are uniform in the film thickness direction, it is also possible to sufficiently cope with the reliability and miniaturization of the semiconductor memory device. On the other hand, the silicon nitride film in which the trap density is uniformly distributed in such a film thickness direction can exhibit favorable charge accumulation capability in the range of 1-20 nm in thickness.

In addition, from the chemical composition profile shown in FIG. 12, in the silicon nitride film of Test Category I (Comparative Example), the oxygen concentration in the film is high near the Si (100) interface and near the surface, but oxygen is almost present near the film center. It can be seen that not. On the other hand, the chemical composition profile shown in FIG. 13 shows that in the silicon nitride film of the test section J, oxygen is present in the vicinity of the center of the film in the vicinity of 20 atomic percent.

From the comparison of FIG. 10 to FIG. 13, when attention is paid to the distribution in the film thickness direction of oxygen in the silicon nitride film, the electron occupancy defect density increases in the region where oxygen is present, for example, even if oxygen exists beyond 20 atomic%. As a result, it has been found that the electron occupancy defect density does not increase in proportion to the increase in oxygen, and the limit is reached. Therefore, dangling bonds generated during the substitution reaction of trivalent nitrogen atoms by divalent oxygen atoms in the silicon nitride film are involved in the generation of electron occupancy defects present in the silicon nitride film. Is guessed.

As described above, the silicon nitride film formed by selecting the plasma CVD conditions using the plasma processing apparatus 100 is a film in which the electron occupancy defect density is controlled with high precision, and has a distribution of trap densities uniform in the thickness direction of the film. will be.

Next, an example in which the method of forming the silicon nitride film according to the present embodiment is applied to the manufacture of a semiconductor device will be described. Here, an n-channel nonvolatile semiconductor memory device is described as an example of a semiconductor device. 14 is an explanatory diagram showing a cross-sectional structure of a nonvolatile semiconductor memory device 200 according to an embodiment of the present invention. 15 to 20 are cross-sectional views for illustrating the manufacturing process of the nonvolatile semiconductor memory device according to the present embodiment.

As shown in FIG. 14, the nonvolatile semiconductor memory device 200 includes, for example, a tunnel oxide film 205, a silicon nitride film 207, and the like sequentially on a p-type silicon substrate (Si substrate) 201 from the bottom. It has the element structure S in which the silicon oxide film 209 and the electrode 211 were formed.

The tunnel oxide film 205 is composed of, for example, a SiO ₂ film or a SiON film having a film thickness of about 0.1 to 10 nm. The silicon nitride film 207 functions as a charge storage layer and is composed of, for example, a SiN film or a SiON film having a film thickness of about 1 to 50 nm. In addition, you may provide two or more silicon nitride films as a charge storage layer. The silicon oxide film 209 is, for example, an SiO ₂ film formed by a CVD method, and functions as a block layer (barrier layer) between the electrode 211 and the silicon nitride film 207. This silicon oxide film 209 has a film thickness of, for example, about 0.1 to 50 nm. The electrode 211 is made of, for example, a polycrystalline silicon film formed by a CVD method and functions as a control gate (CG) electrode. In addition, the electrode 211 may be a film containing a metal such as tungsten, titanium, tantalum, copper, aluminum, gold, or the like. The electrode 211 has a film thickness of, for example, about 0.1 to 50 nm. The electrode 211 is not limited to a single layer, but has a laminated structure containing tungsten, molybdenum, tantalum, titanium, their silicides, nitrides, alloys, and the like for the purpose of lowering and increasing the specific resistance of the electrode 211. can do. This electrode 211 is connected to a wiring layer (not shown).

The nonvolatile semiconductor memory device 200 may be formed in a p well or a p-type silicon layer in a semiconductor substrate.

In addition, an element isolation film 203 is formed on the surface of the Si substrate 201, and an active region A in which the nonvolatile semiconductor memory device 200 is formed is partitioned by the device isolation film 203. . In the region around the element structure S in the Si substrate 201, a source region 212 and a drain region 214 are formed. A portion held between the source region 212 and the drain region 214 in the active region A is the channel forming region 216 of the nonvolatile semiconductor memory device 200. In addition, sidewalls 218 are formed at both sides of the element structure S. FIG.

An operation example of the nonvolatile semiconductor memory device 200 having the above structure will be described. First, at the time of data writing, the source region 212 and the drain region 214 are kept at 0 V based on the potential of the Si substrate 201, and a predetermined positive voltage is applied to the electrode 211. Is authorized. At this time, electrons are accumulated in the channel formation region 216 to form an inversion layer, and a part of the electrons in the inversion layer move to the silicon nitride film 207 through the tunnel oxide film 205 by the tunnel effect. The electrons moved to the silicon nitride film 207 are trapped in the trap which is the charge trapping center formed in the silicon nitride film 207, and data is accumulated.

At the time of reading data, either the source region 212 or the drain region 214 is set to 0V based on the potential of the Si substrate 201, and a predetermined voltage is applied to the other side. In addition, a predetermined voltage is also applied to the electrode 211. By applying the voltage in this manner, the amount of current or drain voltage of the channel changes depending on the presence or absence of electrons accumulated in the silicon nitride film 207 and the amount of accumulated electrons. Therefore, by detecting the change in the channel current or the drain voltage, the stored data can be read out.

In erasing data, both the source region 212 and the drain region 214 are set to 0 V based on the potential of the Si substrate 201, and a negative voltage having a predetermined magnitude is applied to the electrode 211. Is applied. By the application of such a voltage, electrons held in the silicon nitride film 207 are taken out to the channel formation region 216 through the tunnel oxide film 205. As a result, the nonvolatile semiconductor memory device 200 returns the electron accumulation amount in the silicon nitride film 207 to a low erase state.

When manufacturing such a nonvolatile semiconductor memory device 200, first, as shown in FIG. 15, on a Si substrate 201, for example, LOCOS (Local Oxidation of Silicon) method, STI (Shallow Tench Isolation) method, or the like. The device isolation film 203 is formed by the method. In addition, in order to adjust the threshold voltage of the nonvolatile semiconductor memory device 200, impurity doping may be performed by a method such as ion implantation.

Next, a silicon oxide film is formed on the surface of the active region A of the Si substrate 201 by, for example, thermal oxidation. As a result, as shown in FIG. 16, a tunnel oxide film 205 is formed. On the other hand, if necessary, the surface of the silicon oxide film may be nitrided to form a silicon oxynitride film (SiON film).

Next, as shown in FIG. 17, the silicon nitride film 207 as a charge storage layer is formed on the tunnel oxide film 205 by the plasma CVD method. In the step of forming the silicon nitride film 207, as described above, the film is formed under a predetermined plasma CVD condition by using the plasma processing apparatus 100 shown in FIG. I can control it.

Next, as shown in FIG. 18, the silicon oxide film 209 is formed on the silicon nitride film 207. Next, as shown in FIG. The silicon oxide film 209 can be formed by, for example, a thermal oxidation method or a CVD method. As shown in Fig. 19, a polysilicon layer, a metal layer, a metal silicide layer, or the like is deposited on the silicon oxide film 209 to form the electrode film 211a. This electrode film 211a can be formed by, for example, a CVD method using a silane-based gas as a raw material.

Next, using the photolithography technique, the electrode film 211a, the silicon oxide film 209, the silicon nitride film 207, and the tunnel oxide film 205 are etched using the patterned resist as a mask. As shown in Fig. 2, a laminated structure of a patterned electrode 211, a silicon oxide film 209, and a silicon nitride film 207 is obtained.

Next, n-type impurities are ion implanted at low concentration into the silicon surface of the active region A through the tunnel oxide film 205 to form an impurity region (n channel). In addition, sidewalls 218 are formed. Then, a high concentration of n-type impurities are implanted into the silicon of the active region A to form the source region 212 and the drain region 214. In this way, the nonvolatile semiconductor memory device 200 having the structure shown in FIG. 14 can be manufactured.

In the above description, the n-channel nonvolatile semiconductor memory device 200 is taken as an example. In the case of the p-channel semiconductor memory device, it is preferable to reverse the impurity conductivity type.

As described above, according to the present embodiment, the plasma density of the silicon nitride film is controlled with high accuracy by selecting the plasma CVD conditions and performing the film formation by using the plasma processing apparatus 100 to achieve a desired trap density distribution, For example, a uniform trap density can be formed in the film thickness direction. The silicon nitride film formed by the method of forming the silicon nitride film according to the present embodiment has excellent characteristics as an insulating film when fabricating various semiconductor devices, and is particularly suitable as a charge storage layer of a nonvolatile semiconductor memory device.

Second Embodiment

Next, referring to Figs. 21 and 22, a second embodiment of the present invention will be described. 21 is an explanatory diagram showing an example of a procedure of a method of forming a silicon nitride film according to the present embodiment. In the method for forming a silicon nitride film according to the present embodiment, the plasma processing apparatus 100 is used to form a film by changing plasma CVD conditions so that two or more layers of silicon nitride films having trap densities of different sizes are formed. There is a characteristic in point.

As shown in FIG. 21, first, the gate valve 17 of the plasma processing apparatus 100 is closed, and the wafer W is carried into the chamber 1 of the plasma processing apparatus 100 from the carry-in / out port 16. As shown in FIG. Then, it mounts on the mounting table 2 (step S11). Next, the exhaust device 24 is operated to exhaust the reduced pressure in the chamber 1 (step S12). The nitrogen-containing gas and the silicon-containing gas are respectively supplied at a predetermined flow rate from the nitrogen-containing gas supply source 19a and the silicon-containing gas supply source 19b of the gas supply mechanism 18 while evacuating the inside of the chamber 1 under reduced pressure. It introduces into (1) (step S13). In this way, the inside of the chamber 1 is adjusted to predetermined pressure.

Next, a microwave of a predetermined frequency generated at the microwave generator 39, for example, 2.45 GHz, is radiated to the space above the wafer W in the chamber 1 through the planar antenna 31 to generate plasma ( Step S14). In plasma, dissociation of source gas advances, and a thin film of silicon nitride Si _x N _y is deposited by reaction of active species such as Si _p H _q , SiH _q , NH _q , and N. In the above steps S13 and S14, plasma CVD is performed by setting gas species, pressure, microwave power, and the like to predetermined conditions (the conditions described in the first embodiment).

Next, the supply of microwaves is stopped to end the formation of the silicon nitride film (step S15). Next, supply of the gas from the gas supply mechanism 18 is stopped (step S16). Thereafter, the inside of the chamber 1 is adjusted by introducing a purge gas such as nitrogen gas into the chamber 1 for a predetermined time (step S17). On the other hand, the adjustment process of this step S17 is not essential.

In the method of forming the silicon nitride film according to the present embodiment, after the step S16 (or step S17), the silicon nitride film is formed under another plasma CVD condition (the conditions described in the first embodiment) again. That is, after completion of the process of step S17 (or step S16), the flow returns to step S13 again to introduce the film forming raw material gas into the chamber to adjust the inside of the chamber to a predetermined pressure. Then, plasma CVD is performed in the order from step S14 to step S17 (or step S16) as described above. However, in this second film forming process, plasma CVD is performed under conditions different from the first film forming process by changing the type of source gas, the set pressure, and the like. Thereby, the silicon nitride film which has a different trap density can be laminated | stacked and formed in the 1st film-forming process and the 2nd film-forming process, respectively. In addition, by depositing these alternately, a plurality of silicon nitride films having different trap densities can be deposited alternately.

On the other hand, in this embodiment, the process from step S13 to step S17 (or step S16) can be repeated three or more times as necessary. Thus, by repeating the film formation under different plasma CVD conditions, silicon nitride films having different trap densities can be deposited sequentially. In the step where all the film forming processes are completed, the process for one wafer W is terminated by carrying out the wafer W in which the silicon nitride film is formed in the chamber 1 in step S18.

In this embodiment, the magnitude of the trap density in the silicon nitride film formed in each film forming step can be controlled by selecting the same conditions as the plasma CVD conditions of the first embodiment. That is, when forming the silicon nitride film with a large trap density, or when forming the silicon nitride film with a small trap density, it can carry out on the conditions similar to the plasma CVD conditions shown by 1st Example, respectively.

In this embodiment, two or more silicon nitride films formed as described above can be used, for example, as a charge storage layer of a nonvolatile semiconductor memory device. Specifically, according to the method for forming the silicon nitride film of the present embodiment, as shown in FIG. 22, for example, the first silicon nitride film 207a having a small trap density, the second silicon nitride film 207b having a large trap density, The nonvolatile semiconductor memory device 200a having a structure in which the third silicon nitride film 207c having a small trap density is laminated can be manufactured. In addition, since the other structure in the nonvolatile semiconductor memory device 200a shown in FIG. 22 is the same as that of the nonvolatile semiconductor memory device 200 shown in FIG. 14, the same code | symbol is attached | subjected and description is abbreviate | omitted. In the nonvolatile semiconductor memory device 200a shown in FIG. 22, three of the first silicon nitride film 207a, the second silicon nitride film 207b, and the third silicon nitride film 207c are formed as charge storage layers. Although the structure which has a silicon nitride film of a layer was made, it is also possible to form the charge accumulation layer of the structure which laminated | stacked four or more silicon nitride films by repeating film-forming by plasma CVD.

As described above, according to the method of forming the silicon nitride film of the present embodiment, by forming a silicon nitride film having a different trap density by laminating, various band engineering is possible in the nonvolatile semiconductor memory device, and the nonvolatile semiconductor is excellent in data retention characteristics. The memory device can be manufactured. In addition, in this embodiment, since the silicon nitride film having two or more layers having different trap densities can be formed in the chamber 1 of the single plasma processing apparatus 100 without exposing it to the atmospheric state, efficient process design can be realized. Can be.

Other configurations, operations, and effects in this embodiment are the same as in the first embodiment.

Third Embodiment

In the second embodiment, a plurality of silicon nitride films are formed by varying the size of the trap density in the silicon nitride film, but it is also possible to form a silicon nitride film having a different silicon concentration in the film instead of the trap density. In the method of forming the silicon nitride film of the third embodiment, the plasma processing apparatus 100 is used to alternately form a silicon nitride film having a high Si concentration and a silicon nitride film having a low Si concentration by changing plasma CVD conditions. The process sequence shown in the flowchart of FIG. 21 in the second embodiment is also applied to this embodiment as it is.

FIG. 23 shows XPS analysis results of a silicon nitride film formed by performing plasma CVD on a Si substrate using a plasma processing apparatus 100. 23 represents the depth of the silicon nitride film measured with an ellipsometer, and the vertical axis represents the ratio (N concentration / Si concentration) of N concentration and Si concentration in the silicon nitride film. The plasma CVD conditions in this test are as follows.

<Plasma CVD condition 4; Low Si Concentration Conditions>

NH ₃ gas flow rate; 800 mL / min (sccm)

Si ₂ H ₆ gas flow rate; 10 mL / min (sccm)

Processing pressure; 126 Pa

Temperature of the mounting table 2; 500 ℃

Microwave power; 2000 W

Microwave power density; 1.67 W / cm 2 (per area 1 cm 2 of planar antenna 31)

<Plasma CVD condition 5; High Si Concentration Conditions>

NH ₃ gas flow rate; 800 mL / min (sccm)

Si ₂ H ₆ gas flow rate; 16 mL / min (sccm)

Processing pressure; 300 Pa

Temperature of the mounting table 2; 500 ℃

Microwave power; 2000 W

Microwave power density; 1.67 W / cm 2 (per area 1 cm 2 of planar antenna 31)

23, the silicon nitride film formed under the plasma CVD condition 5 has a smaller ratio (N concentration / Si concentration) between the N concentration and the Si concentration in the film than the silicon nitride film formed under the plasma CVD condition 4. It can be seen that the Si concentration is high. As described above, when the silicon nitride film is formed using the plasma processing apparatus 100, the Si concentration in the film can be controlled to a desired value by changing the plasma processing conditions.

When the Si concentration of the silicon nitride film to be formed is increased (for example, the Si concentration is in the range of 30 to 80 atomic%, preferably in the range of 40 to 70 atomic%), plasma CVD can be performed under the following conditions. In the source gas, NH ₃ gas is used as the nitrogen-containing gas and Si ₂ H ₆ gas is used as the silicon-containing gas, and the flow rate of the NH ₃ gas is within the range of 10 to 5000 mL / min (sccm), preferably 100 to 1000. In the range of mL / min (sccm), the flow rate of Si ₂ H ₆ gas is set within the range of 1 to 100 m 26 L / min (sccm), preferably within the range of 5 to 20 mL / min (sccm). . At this time, the flow rate ratio (NH ₃ gas flow rate / Si ₂ H ₆ gas flow rate) of NH ₃ gas and Si ₂ H ₆ gas is in the range of 0.1 to 1000 from the viewpoint of forming a silicon nitride film having a high Si density with a uniform film thickness. It is preferable to carry out, and it is more preferable to carry out in the range of 10-300. In addition, the processing pressure is preferably 1 Pa to 1333 Pa, more preferably 50 to 650 Pa.

In addition, in the case of forming a silicon nitride film having a low Si concentration (for example, in a range of 10 to 50 atomic%, preferably in a range of 10 to 45 atomic%), the conditions when the Si concentration is increased It is preferable to adjust the kind, flow volume, flow volume ratio, processing pressure, etc. of raw material gas.

In any of the above cases, the plasma CVD process temperature preferably heats the temperature of the mounting table 2 to 300 ° C or higher, preferably 400 to 600 ° C. In addition, the gap (interval from the lower surface of the transparent plate 28 to the upper surface of the mounting table 2) G in the plasma processing apparatus 100 forms a silicon nitride film with a uniform film thickness and good film quality. From a viewpoint, it is preferable to set to about 50-500 mm, for example.

As described above, in the method of forming the silicon nitride film of the present embodiment, silicon nitride films having different Si concentrations can be alternately laminated by changing the plasma CVD conditions and repeating the film forming process of the silicon nitride film (see FIG. 21). The two or more silicon nitride films formed in this way can be used, for example, as a charge storage layer of a nonvolatile semiconductor memory device. For example, referring to the nonvolatile semiconductor memory device 200a shown in FIG. 22 in the second embodiment, the first silicon nitride film 207a having a low Si concentration and the agent having a high Si concentration are used as charge storage layers. A nonvolatile semiconductor memory device 200a having a structure in which a two-nitride silicon film 207b and a third silicon nitride film 207c having a low Si concentration are stacked can be manufactured. Of course, by repeating the film formation by plasma CVD, it is also possible to form a charge accumulation layer having a structure in which four or more silicon nitride films are laminated.

As described above, according to the method of forming the silicon nitride film of the present embodiment, by forming a silicon nitride film having a different Si concentration by stacking, various band engineering is possible in the nonvolatile semiconductor memory device, and the nonvolatile semiconductor is excellent in data retention characteristics. The memory device can be manufactured. In this embodiment, in the chamber 1 of the single plasma processing apparatus 100, two or more layers of silicon nitride films having different Si concentrations can be formed alternately without being exposed to the atmospheric state, so that efficient process design Can be realized.

Other configurations, operations, and effects in this embodiment are the same as in the first and second embodiments.

In addition, this invention is not limited to the said Example, A various deformation | transformation is possible. For example, in the above embodiment, the method of forming the silicon nitride film of the present invention is applied to the formation of the charge storage layer of the nonvolatile semiconductor memory device to improve the charge retention performance. The present invention is not limited to the nonvolatile semiconductor memory device but can be applied in the manufacture of various semiconductor devices.

On the other hand, when manufacturing a semiconductor device such as a nonvolatile semiconductor memory device, a plurality of film forming apparatuses including the plasma processing apparatus 100 are connected through vacuum without exposing to the atmosphere to form desired films sequentially in each film forming apparatus. It is possible to.

Claims (16)

A method of forming a silicon nitride film in which a source gas containing a nitrogen-containing compound and a silicon-containing compound is plasmalized by microwaves and a silicon nitride film is deposited on a substrate by plasma CVD using the plasma. Setting a substrate in a processing chamber of a plasma processing apparatus for introducing microwaves into the processing chamber by a planar antenna having a plurality of holes; Controlling the conditions of plasma CVD in the plasma processing apparatus so as to control the magnitude of the trap density of the silicon nitride film to be deposited to a predetermined value, and depositing a silicon nitride film on the substrate. Method of forming a silicon nitride film comprising a. The method of claim 1, Plasma under the condition of generating plasma at a processing pressure within the range of 1 Pa to 1333 Pa by using ammonia (NH ₃ ) as the nitrogen-containing compound and disilane (Si ₂ H ₆ ) as the silicon-containing compound. A method of forming a silicon nitride film, which forms the silicon nitride film by CVD. The method of claim 2, A method for forming a silicon nitride film in which the flow rate ratio (NH ₃ flow rate / Si ₂ H ₆ flow rate) of the ammonia (NH ₃ ) and the disilane (Si ₂ H ₆ ) in the source gas is in the range of 0.1 to 1000. The method of claim 1, The silicon nitride film formation method which distributes the trap density of the said silicon nitride film in the range of 1 * 10 <^17> -5 * 10 <^17> cm <^3> eV <^-1> in the thickness direction. The method of claim 4, wherein A method of forming a silicon nitride film in which the film thickness of the silicon nitride film is in a range of 1 to 20 nm. The method of claim 1, Nitrogen (N ₂ ) is used as the nitrogen-containing compound, and disilane (Si ₂ H ₆ ) is used as the silicon-containing compound, so that plasma is generated at a processing pressure within a range of 0.1 Pa to 500 Pa. A method of forming a silicon nitride film, which forms the silicon nitride film by plasma CVD. The method of claim 6, A method for forming a silicon nitride film in which the flow rate ratio (N ₂ flow rate / Si ₂ H ₆ flow rate) of the nitrogen (N ₂ ) and the disilane (Si ₂ H ₆ ) in the source gas is in the range of 0.1 to 5000. The method of claim 1, The process for forming a silicon nitride film when the silicon nitride film is deposited by the plasma CVD is a temperature within a range of 300 ° C to 600 ° C. A method of forming a silicon nitride film in which a source gas containing a nitrogen-containing compound and a silicon-containing compound is plasmalized by microwaves and a silicon nitride film is deposited on a substrate by plasma CVD using the plasma. Setting an object to be processed in a processing chamber of a plasma processing apparatus which introduces microwaves into the processing chamber by a planar antenna having a plurality of holes; In the plasma processing apparatus, depositing a first silicon nitride film having a first trap density on a surface of a substrate by plasma CVD under a first condition; In the plasma processing apparatus, depositing a second silicon nitride film having a second trap density different from the first trap density on the first silicon nitride film by plasma CVD under a second condition different from the first condition; Method of forming a silicon nitride film comprising a. The method of claim 9, The first silicon nitride film uses ammonia (NH ₃ ) as the nitrogen-containing compound, and disilane (Si ₂ H ₆ ) as the silicon-containing compound, at a processing pressure within a range of 1 Pa to 1333 Pa. Formed by generating a plasma, The second silicon nitride film uses nitrogen (N ₂ ) as the nitrogen-containing compound, and disilane (Si ₂ H ₆ ) as the silicon-containing compound, at a processing pressure within the range of 0.1 Pa to 500 Pa. Formed by generating a plasma Formation method of a silicon nitride film. The method of claim 9, A method of forming a silicon nitride film in which at least one trap density of the first silicon nitride film and the second silicon nitride film is distributed within the range of 1 × 10 ¹⁷ to 5 × 10 ¹⁷ cm ^-3 eV ^-1 in the thickness direction thereof. . The method of claim 11, The formation method of the silicon nitride film whose at least one film thickness of the said 1st silicon nitride film and said 2nd silicon nitride film is in the range of 1-20 nm. The method of claim 9, A method of forming a silicon nitride film, which alternately deposits a first silicon nitride film and deposits the second silicon nitride film. Forming a stack of a plurality of insulating films including a silicon nitride film as a charge storage layer having a charge retention capability over a channel formation region of a semiconductor substrate, and forming a gate electrode on the stack As a manufacturing method of a semiconductor memory device, The silicon nitride film is formed by a method of plasmalizing a source gas containing a nitrogen-containing compound and a silicon-containing compound by microwave, and depositing it on a semiconductor substrate by plasma CVD using the plasma. The method of depositing, Setting a semiconductor substrate in a processing chamber of a plasma processing apparatus for introducing microwaves into the processing chamber by a planar antenna having a plurality of holes; Controlling the conditions of plasma CVD in the plasma processing apparatus so as to control the magnitude of the trap density of the deposited silicon nitride film to a predetermined value to deposit the silicon nitride film on the semiconductor substrate; Method of manufacturing a nonvolatile semiconductor memory device comprising a. A laminate of a plurality of insulating films including a semiconductor substrate having a channel forming region on its main surface, a silicon nitride film formed on the channel forming region, and a silicon nitride film as a charge storage layer having a charge holding capability, and a gate electrode formed on the laminate A nonvolatile semiconductor memory device having, The silicon nitride film is formed by a method of converting a source gas containing a nitrogen-containing compound and a silicon-containing compound into a plasma by plasma, and depositing it on a semiconductor substrate by plasma CVD using the plasma, The method of depositing, Setting a semiconductor substrate in a processing chamber of a plasma processing apparatus for introducing microwaves into the processing chamber by a planar antenna having a plurality of holes; Controlling the conditions of plasma CVD in the plasma processing apparatus so as to control the magnitude of the trap density of the deposited silicon nitride film to a predetermined value to deposit the silicon nitride film on the semiconductor substrate; Nonvolatile semiconductor memory device comprising a. A processing chamber for processing a target object using plasma, A planar antenna having a plurality of holes for introducing microwaves into the processing chamber, A gas supply mechanism for supplying a source gas into the processing chamber; An exhaust mechanism for evacuating the inside of the processing chamber under reduced pressure; A temperature adjusting mechanism for adjusting the temperature of the object to be processed; The source gas containing the nitrogen-containing compound and the silicon-containing compound is plasma-deposited by microwaves introduced into the processing chamber by the planar antenna, and deposited when the silicon nitride film is deposited on the substrate by plasma CVD using the plasma. Control section for controlling the conditions of plasma CVD in the plasma processing apparatus so that the magnitude of the trap density of the silicon nitride film to be controlled is a predetermined value Plasma processing apparatus comprising a.

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